Optical imaging system

ABSTRACT

An optical imaging system includes a first lens having negative refractive power, a second lens having negative refractive power, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens. The first to seventh lenses are sequentially disposed from an object side toward an image side. The third lens, the fourth lens, the sixth lens, and the seventh lens are formed of plastic, and the first lens, the second lens, and the fifth lens are formed of glass.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/108,506 filed on Aug. 22, 2018, now U.S. Pat. No. 10,845,575 issuedon Nov. 24, 2020, which claims the benefit under 35 USC 119(a) of KoreanPatent Application No. 1 0-201 7-01 6771 5 filed on Dec. 7, 2017, in theKorean Intellectual Property Office, the entire disclosures of which areincorporated herein by reference for all purposes.

BACKGROUND 1. Field

This application relates to an optical imaging system.

2. Description of the Background

In general, camera modules are mounted in mobile communicationsterminals, computers, vehicles, and the like, enabling the capturing ofimages.

In accordance with the trend for slimmer mobile communicationsterminals, such camera modules have been required to have a small sizeand high image quality.

Meanwhile, a camera module for a vehicle has also been required to havea small size and high image quality to not obstruct a driver's visualfield and spoil a vehicle appearance.

Particularly, a camera used in a rearview mirror of a vehicle should beable to capture a clear image to secure a rear visual field duringdriving of the vehicle, and is thus required to have high image quality.

In addition, a camera used in a vehicle should be able to clearlycapture an image of an object even at night when illumination is low,and thus requires a lens system that has a small size and which maycapture an image in both of a visible wavelength region and a nearinfrared region.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, an optical imaging system includes a first lenshaving negative refractive power, a second lens having negativerefractive power, a third lens, a fourth lens, a fifth lens, a sixthlens, and a seventh lens. The first to seventh lenses are sequentiallydisposed from an object side toward an image side, the third lens, thefourth lens, the sixth lens, and the seventh lens are formed of plastic,and the first lens, the second lens, and the fifth lens are formed ofglass.

Object-side surfaces and image-side surfaces of the first lens and thesecond lens may be spherical surfaces, and object-side surfaces andimage-side surfaces of the third lens, the fourth lens, the fifth lens,the sixth lens, and the seventh lens may be aspherical surfaces.

The third lens, the fourth lens, and the seventh lens may be formed ofplastic having the same optical characteristics.

The sixth lens and the seventh lens may be disposed closer to each otherthan any other lenses to each other.

The sixth lens and the seventh lens may be formed of plastic havingdifferent optical characteristics from each other.

The optical imaging system may further include a stop disposed betweenthe fourth lens and the fifth lens.

In the optical imaging system TTL is a distance from an object-sidesurface of the first lens to an imaging plane of an image sensor, IMGHis a half of a diagonal length of the imaging plane of the image sensor,and TTL/(2*IMGH) may be less than 3.0.

In the optical imaging system f3 is a focal length of the third lens, fis an overall focal length of the optical imaging system including thefirst lens to the seventh lens, and f/f3 may be greater than 0.02 andless than 0.65.

In the optical imaging system f4 is a focal length of the fourth lensand f/f4 may be greater than −0.5 and less than −0.1.

In the optical imaging system f6 is a focal length of the sixth lens andf/f6 may be greater than 0.25 and less than 0.65.

In the optical imaging system f7 is a focal length of the seventh lensand f/f7 may be greater than −0.5 and less than −0.1.

A refractive index of the third lens may be less than 1.64. A refractiveindex of the fourth lens may be less than 1.64. A refractive index ofthe sixth lens may be less than 1.535 and a refractive index of theseventh lens may be less than 1.64.

In another general aspect, an optical imaging system includes a firstlens having negative refractive power and having a meniscus shape, ofwhich an object-side surface is convex, a second lens having negativerefractive power and having both surfaces concave, a third lens, afourth lens, a fifth lens, a sixth lens, and a seventh lens. The firstto seventh lenses are sequentially disposed from an object side towardan image side, the third lens, the fourth lens, the sixth lens, and theseventh lens are formed of plastic, and the first lens, the second lens,and the fifth lens are formed of glass. A distance between the sixthlens and the seventh lens is shorter than between any other lenses, andthe sixth lens and the seventh lens are formed of plastic havingdifferent optical characteristics from each other.

The third lens, the fourth lens, and the seventh lens may be formed ofplastic having the same optical characteristics. The third lens may havea positive refractive power, the fourth lens may have a negativerefractive power, and the seventh lens may have a negative refractivepower.

Both surfaces of the third lens may be convex and both surfaces of thefourth lens may be concave.

An object-side surface and an image-side surface of the first lens maybe spherical surfaces.

An object-side surface and an image-side surface of the second lens maybe spherical surfaces, and object-side surfaces and image-side surfacesof the third lens and the fifth lens may be aspherical surfaces.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a first example of an optical imagingsystem.

FIG. 2 illustrates examples of curves representing aberrationcharacteristics of the optical imaging system illustrated in FIG. 1 .

FIG. 3 is a view illustrating a second example of an optical system.

FIG. 4 illustrates examples of curves representing aberrationcharacteristics of the optical imaging system illustrated in FIG. 3 .

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The drawings may not be to scale,and the relative size, proportions, and depiction of elements in thedrawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent after an understanding of thedisclosure of this application. For example, the sequences of operationsdescribed herein are merely examples, and are not limited to those setforth herein, but may be changed as will be apparent after anunderstanding of the disclosure of this application, with the exceptionof operations necessarily occurring in a certain order. Also,descriptions of features that are known in the art may be omitted forincreased clarity and conciseness.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided merelyto illustrate some of the many possible ways of implementing themethods, apparatuses, and/or systems described herein that will beapparent after an understanding of the disclosure of this application.

In the drawings, the thicknesses, sizes, and shapes of lenses have beenslightly exaggerated for convenience of explanation. Particularly, theshapes of spherical surfaces or aspherical surfaces illustrated in thedrawings are illustrated by way of example. That is, the shapes of thespherical surfaces or the aspherical surfaces are not limited to thoseillustrated in the drawings.

In this application, a first lens refers to a lens closest to an object,while a seventh lens refers to a lens closest to an image sensor.

In addition, a first surface of each lens refers to a surface thereofclosest to an object side (or an object-side surface) and a secondsurface of each lens refers to a surface thereof closest to an imageside (or an image-side surface). Further, all numerical values of radiiof curvature and thicknesses of lenses, image heights (ImgH, a half of adiagonal length of an imaging plane of the image sensor), and the like,are indicated by millimeters (mm), and a field of view (FOV) of anoptical imaging system is indicated by degrees.

Further, in a description for a shape of each of the lenses, the meaningthat one surface of a lens is convex is that a paraxial region portionof a corresponding surface is convex, and the meaning that one surfaceof a lens is concave is that a paraxial region portion of acorresponding surface is concave. Therefore, although it is describedthat one surface of a lens is convex, an edge portion of the lens may beconcave. Likewise, although it is described that one surface of a lensis concave, an edge portion of the lens may be convex.

A paraxial region refers to a very narrow region in the vicinity of anoptical axis.

An aspect of the present disclosure provides an optical imaging systemin which an aberration improvement effect may be increased, a high levelof resolution may be implemented, imaging may be performed even in anenvironment in which illumination is low, and a deviation in resolutionmay be suppressed even over a wide change in temperature.

An optical system in the examples described herein may include sevenlenses.

For example, the optical imaging system may include a first lens, asecond lens, a third lens, a fourth lens, a fifth lens, a sixth lens,and a seventh lens sequentially disposed from the object side.

However, the optical system is not limited to only including the sevenlenses, but may further include other components, if necessary.

For example, the optical imaging system may further include an imagesensor configured to convert an image of a subject incident on the imagesensor into an electrical signal. The image sensor may be configured tocapture an image of an object in a near infrared region as well as avisible light region.

In addition, the optical imaging system may further include a stopconfigured to control an amount of light. For example, the stop may bedisposed between the fourth and fifth lenses.

In the optical imaging system in the examples described herein, some ofthe first to seventh lenses may be formed of plastic, and the othersthereof may be formed of glass. In addition, the lenses formed of glassmay have optical characteristics different from those of the lensesformed of plastic.

For example, the first lens, the second lens, and the fifth lens may beformed of glass, and the third lens, the fourth lens, the sixth lens,and the seventh lens may be formed of plastic.

In addition, in the optical imaging system in the examples describedherein, some of the first to seventh lenses may be aspherical lenses,and the others thereof may be spherical lenses.

As an example, first surfaces and second surfaces of each of the firstlens and the second lens may be spherical surfaces. First and secondsurfaces of the third lens to the seventh lens may be asphericalsurfaces.

That is, the first lens and the second lens may be formed of glass andhave first surfaces and second surfaces which are spherical surfaces,and the fifth lens may be formed of glass and may have a first surfaceand a second surface which are aspherical surfaces.

In addition, the third lens, the fourth lens, the sixth lens, and theseventh lens may be formed of plastic and may have first surfaces andsecond surfaces which are aspherical surfaces.

An aspherical surface of each of the lenses may be represented by thefollowing Equation 1:

$\begin{matrix}{Z = {\frac{cY^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)c^{2}Y^{2}}}} + {AY}^{4} + {BY^{6}} + {CY^{8}} + {DY^{10}} + \ldots}} & (1)\end{matrix}$

In Equation 1, c is a curvature (an inverse of a radius of curvature) ofa lens, K is a conic constant, and Y is a distance from a certain pointon an aspherical surface of the lens to an optical axis in a directionperpendicular to the optical axis. In addition, constants A to D areaspherical coefficients. In addition, Z is a distance between thecertain point on the aspherical surface of the lens at the distance Yand a tangential plane meeting the apex of the aspherical surface of thelens.

The optical imaging system including the first to seventh lenses mayhave negative refractive power/negative refractive power/positiverefractive power/negative refractive power/positive refractivepower/positive refractive power/negative refractive power sequentiallyfrom the object side.

The optical imaging system in the examples described herein may satisfythe following Conditional Expressions 2 through 10:TTL/(2*IMGH)<3.0  (2)0.25<f/f3<0.65  (3)−0.5<f/f4<−0.1  (4)0.25<f/f6<0.65  (5)−0.5<f/f7<−0.1  (6)n3<1.64  (7)n4<1.64  (8)n6<1.535  (9)n7<1.64  (10)

In the above Conditional Expressions 2 through 10, TTL is a distancefrom an object-side surface of the first lens to the imaging plane ofthe image sensor, IMGH is a half of a diagonal length of the imagingplane of the image sensor, f is an overall focal length of the opticalimaging system, f3 is a focal length of the third lens, f4 is a focallength of the fourth lens, f6 is a focal length of the sixth lens, f7 isa focal length of the seventh lens, n3 is a refractive index of thethird lens, n4 is a refractive index of the fourth lens, n6 is arefractive index of the sixth lens, and n7 is a refractive index of theseventh lens.

In the optical imaging system in some examples described herein, aplurality of lenses may perform an aberration correction function tothus increase aberration improvement performance.

In addition, the optical imaging system may have an f-number (Fno) (aconstant indicating brightness of the optical imaging system) of 2.1 orless to thus clearly capture an image of an object even in anenvironment in which illumination is low.

In addition, the optical imaging system may clearly capture the image ofthe object in both of a visible light region and a near infrared region.

Further, in the optical imaging system in some of the examples describedherein, the first lens, the second lens, the fourth lens, and the fifthlens may be configured as spherical lenses to thus reduce costs formanufacturing the optical imaging system.

In addition, in the optical imaging system in some of the examplesdescribed herein, since the first lens, the second lens, and the fifthlens are formed of glass having a relatively small coefficient ofthermal expansion and the third lens, the fourth lens, the sixth lens,and the seventh lens are formed of plastic, a constant resolution may bemaintained even over a temperature range of about −40 to about 80° C.Therefore, the optical imaging system in some of the examples describedherein may implement a high level of resolution even in an environmentin which a temperature changes over a wide range.

A housing in which the first lens to the seventh lens are disposed maybe formed of plastic, and the housing may shrink or expand according toa change in temperature of the surrounding environment. Therefore, adistance between the seventh lens and the image sensor may be changed bythe deformation of the housing according to the change in temperature,which may result in a problem that a focus does not converge properly.

However, in the optical imaging system in some of the examples describedherein, since the third lens, the fourth lens, the sixth lens, and theseventh lens are formed of plastic, the third lens, the fourth lens, thesixth lens, and the seventh lens may shrink or expand according to thechange in temperature of the surrounding environment.

Therefore, by designing an amount of deformation of the third lens, thefourth lens, the sixth lens, and the seventh lens in consideration of anamount of shape deformation of the housing according to the change intemperature, a focus position may not be changed even in a case in whichthe temperature is changed.

That is, the optical imaging system in some of the examples describedherein may be configured so that a variation of the distance between theseventh lens and the image sensor according to the change in temperaturecorresponds to a variation of the focus position according to the changein temperature.

An optical imaging system according to a first example disclosed hereinwill be described with reference to FIGS. 1 and 2 .

The optical imaging system according to the first example may include anoptical system including a first lens 110, a second lens 120, a thirdlens 130, a fourth lens 140, a fifth lens 150, a sixth lens 160, and aseventh lens 170, and may further include a stop ST, an optical filter180, and an image sensor 190.

Lens characteristics (radii of curvature, thicknesses of lenses ordistances between the lenses, refractive indices, and Abbe numbers) ofeach lens are shown in Table 1.

Meanwhile, the image height may be about 3.3 mm to about 3.4 mm.

TABLE 1 f = 2.2, Fno = 2.07, FOV = 188° Surface No. Radius of CurvatureThickness or Distance Refractive Index Abbe Number Object InfinityInfinity  1 First Lens 11.4930 1.2600 1.7725 49.6  2 3.1700 2.2251  3Second Lens −55.8621 0.7000 1.6204 60.3  4 2.9010 0.4724  5 Third Lens4.4159 2.0000 1.632 23.0  6* −8.5489 0.2000  7* Fourth Lens −8.50000.8000 1.632 23.0  8* 10.3259 0.2000  9 Stop Infinity 0.2000 10* FifthLens 9.4642 2.6000 1.4971 81.5 11* −2.9190 0.1100 12* Sixth Lens 4.92093.1536 1.5311 55.7 13* −4.9271 0.1000 14* Seventh Lens −4.2500 0.95001.632 23.0 15* −27.4167 1.1415 16 Optical Filter Infinity 0.8000 1.516764.1 17 Infinity 1.2769 18 Imaging Plane Infinity −0.0100

In surface numbers of Table 1, the notation * indicates an asphericalsurface.

In the first example, the first lens 110 may have negative refractivepower, and have a meniscus shape, of which an object-side surface isconvex. For example, a first surface of the first lens 110 may be convexin the paraxial region, and a second surface thereof may be concave inthe paraxial region.

The second lens 120 may have negative refractive power, and bothsurfaces thereof may be concave. For example, first and second surfacesof the second lens 120 may be concave in the paraxial region.

The third lens 130 may have positive refractive power, and both surfacesthereof may be convex. For example, first and second surfaces of thethird lens 130 may be convex in the paraxial region.

The fourth lens 140 may have negative refractive power, and bothsurfaces thereof may be concave. For example, first and second surfacesof the fourth lens 140 may be concave in the paraxial region.

The fifth lens 150 may have positive refractive power, and both surfacesthereof may be convex. For example, first and second surfaces of thefifth lens 150 may be convex in the paraxial region.

The sixth lens 160 may have positive refractive power, and both surfacesthereof may be convex. For example, first and second surfaces of thesixth lens 160 may be convex in the paraxial region.

The seventh lens 170 may have negative refractive power, and have ameniscus shape of which an image-side surface is convex. For example, afirst surface of the seventh lens 170 may be concave in the paraxialregion, and a second surface thereof may be convex in the paraxialregion.

Meanwhile, the first and second surfaces of the third lens 130 to theseventh lens 170 may have aspherical coefficients as illustrated inTable 2.

TABLE 2 5 6 7 8 10 11 12 13 14 15 K  0.440136  6.848888  6.135658 1.33456 15 −2.49737 −4.74098  0.30031  0.763848 18.52056 A  0.005715 0.02412  0.010521  0.002348  0.006184 −0.00795  0.003907 −0.02091−0.00098  0.017304 B −3.23E−05 −0.00466 −0.00776 −0.00388 −0.00117 0.000652 −0.00026  0.004831  0.000503 −0.00311 C  0.000163  0.000627 0.000145  0.001091  0  0 −5.16E−06 −0.00049 1.71E−06  0.000286 D−2.86E−05 −0.00046 −0.00032 −0.00022  0  0  1.85E−07 2.37E−05 5.83E−06−1.10E−05

In addition, the first lens 110 and the second lens 120 may be sphericallenses and may be formed of glass. The fifth lens 150 may be anaspherical lens and may be formed of glass. The third lens 130, thefourth lens 140, the sixth lens 160, and the seventh lens 170 may beaspherical lenses and may be formed of plastic.

In addition, the third lens 130, the fourth lens 140, the sixth lens160, and the seventh lens 170 may be formed of plastic having the sameoptical characteristics.

Meanwhile, the sixth lens 160 and the seventh lens 170 may be disposedto be close to each other. For example, among the distances between therespective lenses, a distance between the sixth lens 160 and the seventhlens 170 may be the shortest. In addition, the sixth lens 160 and theseventh lens 170 may be formed of plastic having different opticalcharacteristics.

The sixth lens 160 and the seventh lens 170 formed of plastic havingdifferent optical characteristics may be disposed to be closer to eachother than any other lenses to each other to improve chromaticaberration correction performance.

In addition, the stop ST may be disposed between the fourth lens 140 andthe fifth lens 150.

In addition, the optical imaging system configured as described abovemay have aberration characteristics illustrated in FIG. 2 .

An optical imaging system according to a second example disclosed hereinwill be described with reference to FIGS. 3 and 4 .

The optical imaging system according to the second example may includean optical system including a first lens 210, a second lens 220, a thirdlens 230, a fourth lens 240, a fifth lens 250, a sixth lens 260, and aseventh lens 270, and may further include a stop ST, an optical filter280, and an image sensor 290.

Lens characteristics (radii of curvature, thicknesses of lenses ordistances between the lenses, refractive indices, and Abbe's numbers) ofeach lens are shown in Table 3.

Meanwhile, the image height may be about 3.3 mm to about 3.4 mm.

TABLE 3 f = 2.2, Fno = 2.06, FOV = 188° Surface No. Radius of CurvatureThickness or Distance Refractive Index Abbe Number Object InfinityInfinity  1 First Lens 12.0632 1.2600 1.7725 49.6  2 3.1700 2.2102  3Second Lens −73.9693 0.7000 1.6204 60.3  4 2.9163 0.5551  5 Third Lens4.3464 2.0000 1.632 23.0  6* −32.2432 0.2000  7* Fourth Lens −21.43170.8000 1.632 23.0  8* 11.6389 0.2008  9 Stop Infinity 0.2000 10* FifthLens 9.8550 2.6000 1.4971 81.5 11* −3.1499 0.1100 12* Sixth Lens 4.72103.0489 1.5311 55.7 13* −4.6500 0.1000 14* Seventh Lens −4.2500 0.95001.632 23.0 15* −32.2039 1.1415 16 Optical Filter Infinity 0.8000 1.516764.1 17 Infinity 1.4878 18 Imaging Plane Infinity −0.0100

In surface numbers of Table 3, the notation * indicates an asphericalsurface.

In the second example, the first lens 210 may have negative refractivepower, and have a meniscus shape, of which an object-side surface isconvex. For example, a first surface of the first lens 210 may be convexin the paraxial region, and a second surface thereof may be concave inthe paraxial region.

The second lens 220 may have negative refractive power, and bothsurfaces thereof may be concave. For example, first and second surfacesof the second lens 220 may be concave in the paraxial region.

The third lens 230 may have positive refractive power, and both surfacesthereof may be convex. For example, first and second surfaces of thethird lens 230 may be convex in the paraxial region.

The fourth lens 240 may have negative refractive power, and bothsurfaces thereof may be concave. For example, first and second surfacesof the fourth lens 240 may be concave in the paraxial region.

The fifth lens 250 may have positive refractive power, and both surfacesthereof may be convex. For example, first and second surfaces of thefifth lens 250 may be convex in the paraxial region.

The sixth lens 260 may have positive refractive power, and both surfacesthereof may be convex. For example, first and second surfaces of thesixth lens 260 may be convex in the paraxial region.

The seventh lens 270 may have negative refractive power, and have ameniscus shape of which an image-side surface is convex. For example, afirst surface of the seventh lens 270 may be concave in the paraxialregion, and a second surface thereof may be convex in the paraxialregion.

Meanwhile, the first and second surfaces of the third lens 230 to theseventh lens 270 may have aspherical coefficients as illustrated inTable 4.

TABLE 4 5 6 7 8 10 11 12 13 14 15 K  0.157622 0  0 0 15 −1.44397−4.84012  0.225957 0.905192 61.64189 A  0.006202 0.0127 −0.005170.000124  0.009688 −0.00285  0.003132 −0.01954 0.00075  0.018517 B−0.00026 0.000346  0 0 −0.00138  0.000269 −0.00027  0.004597 0.00019−0.00326 C  0.000211 0  0 0  0  0 −2.13E−05 −0.00049 3.60E−35  0.000293D −378E−05 0  0 0  0  0 −9.81E−07 2.33E−05 5.70E−06 −1.15E−05

In addition, the first lens 210 and the second lens 220 may be sphericallenses and may be formed of glass. The fifth lens 250 may be anaspherical lens and may be formed of glass. The third lens 230, thefourth lens 240, the sixth lens 260, and the seventh lens 270 may beaspherical lenses and may be formed of plastic.

In addition, the third lens 230, the fourth lens 240, the sixth lens160, and the seventh lens 270 may be formed of plastic having the sameoptical characteristics.

Meanwhile, the sixth lens and the seventh lens 270 may be disposed so asto be close to each other. For example, among the distances between therespective lenses, a distance between the sixth lens 260 and the seventhlens 270 may be the shortest. In addition, the sixth lens 260 and theseventh lens 270 may be formed of plastic having different opticalcharacteristics.

The sixth lens 260 and the seventh lens 270 formed of plastic havingdifferent optical characteristics may be disposed to be closer to eachother than any other lenses to each other to thus improve chromaticaberration correction performance.

In addition, the stop ST may be disposed between the fourth lens 240 andthe fifth lens 250.

In addition, the optical imaging system configured as described abovemay have aberration characteristics illustrated in FIG. 4 .

As set forth above, in the optical imaging systems in the examplesdisclosed herein, an aberration improvement effect may be increased, ahigh level of resolution may be implemented, imaging may be performedeven in an environment in which illumination is low, and a deviation inresolution may be suppressed even over a wide change in temperature.

While this disclosure includes specific examples, it will be apparentafter an understanding of the disclosure of this application thatvarious changes in form and details may be made in these exampleswithout departing from the spirit and scope of the claims and theirequivalents. The examples described herein are to be considered in adescriptive sense only, and not for purposes of limitation. Descriptionsof features or aspects in each example are to be considered as beingapplicable to similar features or aspects in other examples. Suitableresults may be achieved if the described techniques are performed in adifferent order, and/or if components in a described system,architecture, device, or circuit are combined in a different manner,and/or replaced or supplemented by other components or theirequivalents. Therefore, the scope of the disclosure is defined not bythe detailed description, but by the claims and their equivalents, andall variations within the scope of the claims and their equivalents areto be construed as being included in the disclosure.

What is claimed is:
 1. An optical imaging system comprising: a firstlens comprising negative refractive power; a second lens comprisingrefractive power; a third lens comprising positive refractive power; afourth lens comprising negative refractive power; a fifth lenscomprising refractive power; a sixth lens comprising positive refractivepower; and a seventh lens comprising negative refractive power, whereinthe first to seventh lenses are sequentially disposed from an objectside toward an image side, wherein TTL/(2*IMGH)<3.0 is satisfied, whereTTL is a distance from an object-side surface of the first lens to animaging plane of an image sensor, and IMGH is a half of a diagonallength of the imaging plane of the image sensor, and wherein−0.5<f/f4<−0.1 is satisfied, where f4 is a focal length of the fourthlens, and f is an overall focal length of the optical imaging system. 2.The optical imaging system of claim 1, wherein the second lens comprisesa concave image-side surface.
 3. The optical imaging system of claim 1,wherein the third lens comprises a convex object-side surface and aconvex image-side surface.
 4. The optical imaging system of claim 1,wherein the fourth lens comprises a concave object-side surface.
 5. Theoptical imaging system of claim 1, wherein the fifth lens comprises aconvex image-side surface.
 6. The optical imaging system of claim 1,wherein the sixth lens comprises a convex object-side surface and aconvex image-side surface.
 7. The optical imaging system of claim 1,wherein n3<1.64 is satisfied, where n3 is a refractive index of thethird lens.
 8. The optical imaging system of claim 1, wherein n7<1.64 issatisfied, where n7 is a refractive index of the seventh lens.
 9. Theoptical imaging system of claim 1, wherein n7<1.64 is satisfied, wheren7 is a refractive index of the seventh lens.
 10. An optical imagingsystem comprising: a first lens comprising negative refractive power; asecond lens comprising refractive power; a third lens comprisingpositive refractive power; a fourth lens comprising negative refractivepower; a fifth lens comprising refractive power; a sixth lens comprisingpositive refractive power; and a seventh lens comprising negativerefractive power, wherein the first to seventh lenses are sequentiallydisposed from an object side toward an image side, wherein−0.5<f/f4<−0.1 is satisfied, where f4 is a focal length of the fourthlens, and f is an overall focal length of the optical imaging system,and wherein n3<1.64 is satisfied, where n3 is a refractive index of thethird lens.
 11. The optical imaging system of claim 10, wherein thesecond lens comprises a concave image-side surface.
 12. The opticalimaging system of claim 10, wherein the third lens comprises a convexobject-side surface and a convex image-side surface.
 13. The opticalimaging system of claim 10, wherein the fourth lens comprises a concaveobject-side surface.
 14. The optical imaging system of claim 10, whereinthe fifth lens comprises a convex image-side surface.
 15. The opticalimaging system of claim 10, wherein the sixth lens comprises a convexobject-side surface and a convex image-side surface.
 16. An opticalimaging system comprising: a first lens comprising negative refractivepower; a second lens comprising refractive power; a third lenscomprising positive refractive power; a fourth lens comprising negativerefractive power; a fifth lens comprising refractive power and a conveximage-side surface; a sixth lens comprising positive refractive power;and a seventh lens comprising negative refractive power, wherein thefirst to seventh lenses are sequentially disposed from an object sidetoward an image side, wherein TTL/(2*IMGH)<3.0 is satisfied, where TTLis a distance from an object-side surface of the first lens to animaging plane of an image sensor, and IMGH is a half of a diagonallength of the imaging plane of the image sensor, and wherein n3<1.64 issatisfied, where n3 is a refractive index of the third lens.
 17. Theoptical imaging system of claim 16, wherein the second lens comprises aconcave image-side surface.
 18. The optical imaging system of claim 16,wherein the third lens comprises a convex object-side surface and aconvex image-side surface.
 19. The optical imaging system of claim 16,wherein the fourth lens comprises a concave object-side surface.
 20. Theoptical imaging system of claim 16, wherein the sixth lens comprises aconvex object-side surface and a convex image-side surface.